Encyclopedia  |   World Factbook  |   World Flags  |   Reference Tables  |   List of Lists     
   Academic Disciplines  |   Historical Timeline  |   Themed Timelines  |   Biographies  |   How-Tos     
Sponsor by The Tattoo Collection
TI99/4A
Main Page | See live article | Alphabetical index

TI99/4A

This article should be merged with  Texas Instruments TI-99/4A

The TI99/4A is a home computer introduced by Texas Instruments in June 1979.

The TI99/4A had a 16-bit TMS-9900 CPU running at 3.3 MHz. This was one of the first 16-bit microprocessors to be made. However, apart from a very small amount of memory, the processor communicated with the rest of the console using an 8 bit data path. Therefore it was substantially slower than a true 16-bit microcomputer. However, the 16 bits were used to make speech synthesis possible, and could also be used by an experienced programmer to speed up some machine code programs.

Because the machine only had 16 KB of RAM the TI99/4A's coprocessor, a TMS-9918, had its own RAM referred to as VDP RAM (visual display processor RAM). This 16 KB of memory could not be directly addressed by the CPU. The VDP was used to provide sprite support.

The VDP RAM was used for screen display, variables, and user program which the main processor cannot directly address. Data was transferred between the VDP and the CPU two bytes at a time, which did not serve as a particularly fast means of communication and no doubt contributed to the slow speed of the 4A.

As there was no realistic amount of RAM addressable by the CPU, machine code programs would not run unless more RAM was added in the form of either the 32 KB expansion card or the 4 KB mini memory module.

The CPU, motherboard, and cartridge drive were built into a single unit with the keyboard.

Peripherals included a 5¼" floppy disk drive, an RS-232 interface, an in-line RS-232 speech synthesizer module, and a 32 KB memory expansion card.

Early models included a built-in equation calculator, but by 1984 this feature had been discontinued.